In recent years, natto has drawn attention by a boom in health care, and studies on natto mucilage have also progressed. The natto mucilage is mainly constituted of poly-γ-glutamic acid produced by Bacillus subtilis var. natto, i.e. a bacterium belonging to species Bacillus subtilis (hereinafter, “Bacillus” may be abbreviated as “B.” in some cases), and further, various uses of poly-γ-glutamic acid itself have been found out.
For example, Japanese publication of unexamined application No. 2000-72652 discloses the use of poly-γ-glutamic acid as cosmetics based on an excellent water-retaining property thereof. In addition, poly-γ-glutamic acid is also expected for use as environment-friendly new material as well as polylactic acid, since poly-γ-glutamic acid is biodegradable. Further, poly-γ-glutamic acid is highly useful, since poly-γ-glutamic acid is a nonrigid plastic, whereas biodegradable polyester materials such as polylactic acid are fundamentally rigid plastics.
In a process for producing poly-γ-glutamic acid, a bacterium belonging to genus Bacillus has been conventionally used. For example, according to Japanese publication of unexamined application No. 2000-333690, it is said that poly-γ-glutamic acid could be more efficiently produced by using a bacterium belonging to genus Bacillus capable of producing poly-γ-glutamic acid and having deleted or decreased glutamic acid synthetase activity, compared to a process using normal bacteria belonging to genus Bacillus. However, a large amount of antibiotics should be added to a culture medium which is a field for production of poly-γ-glutamic acid and the fear of secondary contamination with recombinant products is not avoidable in the technology.
In the publication of No. 2000-333690, the bacteria to be used is comprehensively described as “the genus Bacillus”, and B. licheniformis, B. anthracis and B. megaterium other than B. subtilis are disclosed. However, the strains specifically exemplified therein are only strains belonging to species B. subtilis known as Bacillus natto, and the strain used in Examples is only bacteria belonging to species B. subtilis. 
In addition, among the bacteria belonging to genus Bacillus described in the publication of No. 2000-333690, investigation on productivity of poly-γ-glutamic acid by B. megaterium has not been substantially carried out so far, and even superiority or inferiority as a poly-γ-glutamic acid-producing species and characteristics thereof have not yet been known.
The poly-γ-glutamic acid found widely in the natural world tend to be a hybrid polymer including both of D-glutamic acid and L-glutamic acid in many cases. For example, the poly-γ-glutamic acid produced by a bacterium belonging to species Bacillus subtilis, which is typically Bacillus natto, contains approximately equivalent amounts of L-glutamic acid and D-glutamic acid, or contains D-form in a slightly much more amount (refer to M. Ashiuchi et al., Appl. Microbiol. Biotechnol., vol. 57, pp. 764-769 (2001)).
It is common that the higher the optical purity of a polymer material including a compound having an optical isomer is, the more excellent the characteristics thereof is. For example, the poly-γ-glutamic acid having a high content of L-glutamic acid has higher water-retentivity. Moreover, the poly-γ-glutamic acid having a high content of one optical isomer is extremely excellent as a plastic material, since the crystallinity and intensity of such a material are highly increased.
There is a poly-γ-glutamic acid having high optical purity among poly-γ-glutamic acid obtained from the natural world. For example, Natrialba aegyptiaca, which is a kind of halophilic archaea, produces L-glutamic acid-rich poly-γ-glutamic acid in order to protect itself from a dehydration phenomenon which occurs under extreme environment where the salt concentration is extremely high. In general, the poly-γ-glutamic acid having low optical purity produced by a bacterium belonging to species B. subtilis rapidly loses water-retentivity, when salts coexist. On the other hand, the poly-γ-glutamic acid having high optical purity derived from halophilic archaea has an extremely excellent water-retaining action. Therefore, it was expected that the poly-γ-glutamic acid having higher quality can be produced by using halophilic archaea.
However, the productivity of halophilic archaea for poly-γ-glutamic acid is far inferior to Bacillus natto and the like. In addition, poly-γ-glutamic acid is almost not produced, when halophilic archaea are cultivated in a liquid culture medium which is suitable for mass production. It is practically concluded that halophilic archaea are not suitable for production of poly-γ-glutamic acid having high optical purity.
There are quite a few bacteria which produce poly-γ-glutamic acid regardless of addition or no addition of L-glutamic acid among species B. subtilis (refer to Y. Ito, et al., Biosci. Biotechnol. Biochem., vol. 60, pp. 1239-1242 (1996)). In this case, production of poly-γ-glutamic acid is frequently started at the middle stage of culture, and the viscosity of the culture medium is increased in association with the production, resulting in the state where dissolved oxygen is decreased, which is fatal for the growth of aerobic bacteria belonging to species B. subtilis (refer to A. M. Cromwick, Biotechnol. Bioeng., vol. 50, pp. 222-227 (1996)). As a result, the bacterial cells cannot be obtained in a sufficient amount, and more efficient production of poly-γ-glutamic acid becomes difficult.